Astigmatism results from refractive errors caused by an asymmetric or irregularly shaped cornea or changes in the curvature of the lens inside the eye affecting the bending or refraction of light in the eye. Astigmatism usually causes blurred or distorted vision at all distances and where uncorrected, can lead to eyestrain, headaches and fatigue with prolonged visual tasks. It has been reported that up to 95% of eyes have some amount of astigmatism, with more than 28% of children between the ages of 5 to 17 and about 15% to 30% of adults have astigmatism of 1 diopter or greater. See J. B. Rubenstein, Today's Peripheral Corneal Relaxing incision, in Cataract & Refractive Surgery Today, pages 26-28, May 2014.
Astigmatism can be corrected during cataract surgery by placing the natural lens with a correcting toric intraocular lens (IOL) or through relaxing the curvature of the cornea by making paired arcuate incisions in the limbus or cornea of the eye using procedures such as limbal relaxing incision (LRI), astigmatic keratotomy (AK) or femtosecond laser assisted astigmatic keratotomy (fAK). These act to compensate for the corneal astigmatism and astigmatism resulting from the cataract incision(s). Current methods to correct astigmatism have limited effectiveness, as use of relaxing incisions is not always possible due to interfering cataract incisions, and both relaxing incision and toric IOLs usually provide only discrete astigmatism correcting power.